WO 2005023451 (MAIKO ENGINEERING GMBH.). 2005 Mar. 17. proposes a metal closure blank, which has an external radius adjacent to its cut edge. This external radius has been found to prevent the formation of “angel hairs”. However, at production speeds (about 1200 closures per minute), the external radius causes a number of problems with conventional tooling.
Conventional closure blanks have a cylindrical side-wall, which closely matches the side-wall of the cavity in the press and thus, the closure blank is retained in the cavity until the press parts are separated and the part carrying the closure blank reaches “top dead centre”. Once this position is reached, the closure blank is ejected from the press by means of “press air”. Where the closure blank has an external radius (to prevent the formation of “angel hairs”), the external radius creates a looser seat in the press cavity and interferes with press air as the press parts are separated after formation of the closure blank. Thus, the closure blank tends to twist uncontrollably and fall out of the press as the press parts are separated.
WO 200249787 (DAYTON SYSTEMS GROUP, INC.). 2002 Jun. 27. describes a press arrangement suitable for production of metal closure blanks (closure cup) having such an outward curled rim. The metal closure blank (closure cup) is biased against part of the forming punch by a first airstream introduced into the cavity within the underside of the cap. As the punch reaches “top dead centre”, the blank (closure cap) is ejected from the punch by a second airstream.
A further problem is encountered during transport of the closure blanks between production stages. An air transport system is conventionally used for this purpose, in order to increase production speeds. Known air transport systems comprise a base plate, sidewalls and a top plate and an air stream passes through the volume so defined, carrying the closure blanks on a cushion of air. When closure blanks having an external radius at their cut edge are transported in such an air transport system, the air flow catches under the external radius and tends to flip or tilt the closure blanks. Thus, such closure blanks “dance” around uncontrollably in the air stream and jostle one another, damaging the thin polymer coating thereon.
U.S. Pat. No. 4,655,677 (PRECISION METAL FABRICATORS, INC.). 1987 Apr. 7. describes a similar problem, encountered when trying to transport container ends through such a conventional air conveyor system. This patent describes how stacks of container ends may be successfully transported in an air conveyer system. In this system, the top cover of the conveyor is spaced above the stack of container ends at a height which is less than the overlap of the nested container ends, thereby ensuring that the container ends remain in their respective stacks when subjected to lateral forces.